Change pitch propeller



- Jan. 21, 1936. G. F. McDOUGALL CHANGE PITCH PROPELLER 5 Sheets-Sheet lFiled 1935 F 12v VENTOR j e fWi Q Jan. 21 1936. MCDOUGALL 2,028,463

CHANGE PITCH PROPELLER Filed Jan. 7, 1935 5 Sheets-Sheet 2 Jan. 21,1936.

G F. M DOUGALL v CHANGE PITCH PROPELLER 5 Sheets-Sheet 5 Filed Jan. '7,1935 IN VENTOR Jan. 21, 1936. F, MCDOUGALL 7 2,028,463

CHANGE PITCH PROPELLER File d Jan. 7,' 1955 5 Sheets-Sheet 4 Jan..21,1936. MCDOUGALL 2,028,463

CHANGE PITCH PROPELLER NV VENTOR Patented Jan. 21, 1936 UNITED STATESCHANGE PITCH PROPELLER George F. McDougall, Portland, Oreg., assignor toEdwin T. Hodge, Portland, Oreg.

Application January 7, 1935, Serial No. 657

16 Claims.

My invention relates to devices for changing the pitch or lead of anairplane propeller from a low or starting pitch to a high or cruisingpitch, changing back as required and'locking the propeller securely inselected pitch.

Various devices have been proposed for variable pitch propellers and itis well known that the desirable propeller pitch for landing andtake-off is different from the pitch desired for cruising. 10 I provide,positively, for only two pitches since a greater number is seldomnecessary or desirable.

One of the objects of my invention is a propeller that has a minimum ofmoving parts with complete absence of thrust bearingsand parts that aredifiicult to maintain.

Another object of my invention is a pitch change device that can only bechanged from low to high pitch when the airplane to which 20 it isattached is traveling through the air at considerable speed.

Another object of my invention is a pitch change device that willinstantly and automatically resume low pitch characteristics when theengine is idling as for examplewhen the airplane is cruising and thepropeller speed is reduced toa point less than the air speed,momentarily, or when the propeller is at rest as for example when themotor is not running. 30 Another object of my invention is a pitchchange device wherein the power of the engine is utilized to change fromone pitch to another.

A most important object of my invention is a pitch change device whereinwhen positively acting the propeller blades are firmly locked inselected position and will therefore remain in that position so long asthe propeller is pulling or pushing the plane, but will automaticallyunlock preparatory to a change of pitch ii the engine 40 is momentarilyidled while proceeding through the air, and that will lock in eitherpitch position the instant any load is accepted by the propeller blades.

Another object is a pitch change device that is equally suited for atwo, three or four blade propeller without the addition of any moremoving parts to control the larger number of blades.

Another object is a device of the character described wherein the changefrom low to high pitch is practically instantaneously effected by enginepower and controlled by a small .easily operated lever or pedal.

Another important object of this invention is a device that will advanceeach propeller blade exactly as much as any other blade, so that thepitch is precisely predetermined, to avoid unequal loading andconsequent fluttering of the blades, and will always have a workablepitch in case of complete failure of the pitch changing device.

These and other objects will be apparent from the followingspecification and claims.

Drawings showing the principal invention herein contained illustrate anddescribe two species of mechanical devices for making use of it. Withthe two types of operating apparatus there is to some extent twodifferent modes of operation and if desired some change in result.

In the drawings, Fig. I is a longitudinal section of my new propellershowing what I consider to be the main invention with the brake type ofoperating device;

Fig. II is a section on line 11-11 of Fig. I;

Fig. III is a view of the same structure shown in Fig. I partlysectioned to show the cam I in operated position that it will assumeunder positive load of the propeller when the blades are being used topropel the plane;

Fig. IV is a section on IVIV of Fig. I to which it must be referred;

Fig. V is the same structure shown in Fig.1I except that it shows theoperated position of the interior parts as they will exist when thepropeller is being operated according to Fig. 111;

Fig. VI is a stretchout of the cam I, which is considered the principalinvention herein, when it is co-operating with the propeller blade, theleading edge of which controls, but showing the blade at rest orrevolving under negative load;

Fig. VII is the same stretchout shown in Fig. VI except that the cam Ihas rotated to change the pitch of the blades and the. blades will beconsidered to be under positive load;

Fig. VIII is a somewhat different arrangement from that shown in Fig.III in that the main invention or cam I contracts to locking positionunder load as hereinafter explained;

Fig. IX is a stretchout of the cam I as it is being used in Fig. VIIIwith the propeller carrying a load;

Fig. X is the same stretchout shown in Fig. IX except that the camI hasrotated to a different position and moved the blades to a higher pitch;

Fig. In is a front view of the propeller hub as shown in Figs. I, III,V111 and XII, to a smaller 50 scale and with propeller blades attached,in this case with the propeller blades having a greater area on thetrailing edge as required in Figs. IX and X on the same sheet;

Fig. XII is a view of substantially the same 6;

structure shown in Fig. I partly in section and delineates a diiferentstructure for controlling the cam I as hereinafter explained in detail;

Fig. XIII is a section on XIJI-XI1I of Fig. XII.

Referring to Fig. I: A driven propeller shaft 2 is made rigid within thenose of the hub 3 and drives through the hub 3 to cause revolution of aplurality of propeller blades 4, rotatively mounted on the hub 3. Withinan appropriate chamber within the hub 3 is a. two-part cam I, arrangedas for example at Ia, with an angular intercepting divisional surface sothat it may be rotated as an unit 'butis freely expansible andcontractible axially within the limits fixed by structure with which itwill contact on expansion and by the two surfaces such as lb coming incontact upon contraction.

The cam I is preferably drum-shaped and may have flanges as shown at Id,and is equipp d with angular cam slots I e and If that are oppositelypitched. On the inner end of the propeller blade, a couple 6 is formed,integral therewith or rigidly attached thereto, one element of whichengages with the slot If, in one part of the cam and the other elementof which engages with the slot Ie in the other part of the cam.

It is evident that a semi-rotation of the cam I with respect to the hub3 will cause an axial part revolution of the blade 4 to change the pitchof the blade.

It is also evident that the absolute limit of pitch change of the blade4 is fixed by the definite ends of the cam slots Ie and I I.

Also if the slots such as Ie and I ,f are -all accurately milled to likeangles and proper length,

then the shift of one propeller blade, 4, must be A precisely the sameas the shift of any other blade co-operating with the cam.

Taking the stretchout shown in Fig. VI and viewing it in connection withFig. I and considering Fig. I to be intended to rotate in a clockwisedirection when looking at the nose of the hub: If the speed of the airscrew advance is less than air speed then the 'two parts of the cam Iwill be in the position shown in Fig. I in the stretchout shown in Fig.VI. This is the condition of negative load and can occur only when thepropeller is proceeding through the air at less than air speed, or atrest. It will be noted that in Fig. VI the superior area of thepropeller blade is toward the leading edge.

The moment that the propeller blades shown in dotted outline in Fig. VIand Fig. VII assume a positive load, whether or not the cam I has beenrotated, the twisting moment on the couple 6 separates the two parts ofthe cam I, axially and engages the locking rings III and II to rearwardof the cam I and Illa. and Ila on the forward end of the cam I.

I I and Ila are rigidly attached to the hub 3 as shown, and Ill and Illaare made a part of the cam I, each part of thecam having its own lookingring. The locking ring will be provided with teeth as shown which may bequite small but the angle of which should be greater than the angle ofthe cam slots Ie and If.

The clearance c is shown somewhat exaggerated in Fig. I and in actualpractice it is arranged so that when the cam I is fully contracted asshown in Fig. I the relatively stationary part such as I I and therelatively movable part such as III will just smoothly clear.

Since the turning moment of revolution applied to the blades comes fromthe hub 3 and not from the cam I there is no tendency to a displacementof revolution on the cam I by reason of the power applied to the blades4 except that incident to the slope or angle of the slots Ia and If.

It will be observed by inspection of Fig. I that the cam I must beretarded with respect to the hub 3 in order to change from low to highpitch, and advanced with respect to the hub 3 to change back from highto low pitch.

with the apparatus as delineated in Fig. I and dependent views, thisretardation is efiected by means of the brake I5, which is attached to arelatively fixed partsuch as the engine hub I6 and which co-operateswith the brake drum II under influence of brake operating means notshown. The brake drum I1 is operatively connected to the cam I by meansof the jaw clutch It will be understood that the brake drum I'I revolvesfreely with the propeller hub when the same is in use and that the brakeI5 remains relatively fixed with suflicient clearance so that there isno frictional load.

No apparatus has been shown for applying the brake I5 to the brake drumII as such appliances are well known, but it is suggested that where thepropellers are remote from the control cabin or cockpit, such as out onthe wings of the plane, that the well known hydraulic brake apparatuswill provide an instantaneous and eflicient way of applying the brake I5to the drum II.

Owing to the tremendous centrifugal loads on propeller blades due tohigh rotation and the very high bending moments at the root of theblades due to torque re-action and air resistance, it is not consideredpracticable to turn the blade 4 in its socket 4a while it is underpositive load.

To use the apparatus delineated in Fig. I and subsidiary drawings theplane will take off with the propeller blade in normal low pitch andafter attaining altitude and having leveled off for flying, the bladesfirmly locked in low pitch as heretofore explained, the plane may benosed down a trifling amount to prevent loss of flying speed, the enginemomentarily throttled, and as the propeller slows down' and reaches airspeed or very slightly below air speed, the turning moment on the areaof the propeller blade will reverse which unlocks the cam I to theposition shown in Fig. I. An instantaneous touch of the brake I5 againstthe brake drum II will retard the cam I to its position of high pitch,compressing the springs 20 and 2| and thus storing the force forreturning the cam l to its normal position, shown in Fig. I..

While holding the braking eifect sufiiciently to maintain compression ofthe springs, 20 and 2|, the pilot guns the engine. The propeller bladeinstantly acts as described for positive load, rocking slightly on itsaxis and relocking the surface I0, II, Illa and Ila into high pitchposition, the action being the same as starting a car on a hill. Thepropeller will thereafter remain locked as long as it is carrying apositive load; and if for any reason, controlled or uncontrollable, thepropeller becomes under negative load, the springs 20 and 2| willinstantly assert themselves to restore the cam I to the position shownin Fig. I and the blades to low pitch as shown in Fig. VI.

Also with this type of change apparatus we assuming a positive load whenwarming up, taking oif or attaining altitude. It .cannot be changed tohigh pitch except when in flight and will not remain in high pitchexcept under con- 5 ditions of positive load, but may be selectively,instantly changed to high pitch at any time when the plane is.proceeding through the air fast enough to sustain itself momentarilywhile the propeller is being changed. In Fig. VIII isfound amodification of the structure shown in Fig. I in that the cam I con- Ytracts to locking position instead of expanding as in Fig. I. Toaccomplish this change we here make the trailing edge of the blade ofthegreatest area as shown in Fig. XI which exactly reverses theconditions obtaining in Fig. I considered in view of the stretchoutshown in Figs. VI and VII, the direction of rotation remaining the same,clockwise, as assumed for Fig. I. 1

It is thought that no further explanation of these views is necessary.Neither is it thought that it is necessary for a-further detaileddescription of the couple, 6, since theterm couple" is well known toengineers and the drawings delineate a desirable shape where the balanceof the apparatus is as shown in the several views.

Due to air compression on the-rear of the blade/ and a vacuum on thetrailing edge occasioned by cavitation in front of the blade, there isnornially a turning moment on a symmetrical blade in the vsa inedirection as obtains-when the trailing edge of the blade has thegreatest area. .This is true while the blade ispulling positively'but isnot true when the blade is drifting or running at or less than airspeed.

Hence it will be necessary if it is desired that the trailing edgecontrol the lock thatit be made of somewhat greater area than theleading edge. A somewhat larger disproportionate area will be requiredif the leading edge of the blade is to control as shown in'Fig. In Fig.XII is shown another apparatus for ,rotating the cam. Itwill beconsidered that the apparatus for rotating the cam delineated in Figs.XII and XIH is diagrammatic in its entirety. The cam will be the same inoperating principle as that shown in Fig. I orit may be made according'to that shown in Fig. VIII. In Fig. XIIand somewhat to the rearward,the cam is shown as provided with a" spur gear 25 which coeoperates withthe spur pinion 26 mounted upon a shaft, 21, journaled in the body ofthe' hub 3; the shaft rotatively supporting a friction wheel, 28.Revolution of this friction wheel will displace the cam with respect tothe hub 3 and'the blades 4.

Rotation is here shown,

, diagrammatically, to be accomplished by contacting'either the ring29-or the ring 30, each of which is equipped with a friction track arrangedfor'sliding axiallyinto frictional engagement with the friction wheel28. under the influence of the levers 3| and 3-2. These rings may beoperated by hydraulic or other convenient transmission means. It willbedesirable tohave a..high ratio of speed reduction between the'shaft 21and the cam I so that the change from high to low pitch, or reversely,may be accomplished over a sumcient period of time to .allow the pilot.some choice in the amount of pitch change movement applied to the cam I."Itwill lock in any at tained position as described when positive loadis restored.

75 In this respect the device'inay be to somede- 3 gree variable asdistinguished from the twopitch propelleras delineated in Fig. I.

If the element-30 is engaged withthe friction wheel 28, it will revolvein one direction and if the element 29 is engaged it will revolve in the5 opposite direction, but the load heretofore mentioned, due to torqueand centrifugal loading effeet on the blades may still prevent anysatisfactory shifting of the blades without reducing propeller speed toapproximately air speed, when the bending moment and the centrifugalloading will be greatly reduced.

With the apparatus just described it will be better' to make the bladesso that a leading or a trailing edge of superior area will move the caminto locked position because, being impossible to make two bladesexactly alike, there is always some vibration and vibration tend todisturb the relation of the cam to the blades unless a positivelock isused.

Having delineated and described the best methods whereby I propose tocarry out my invention at this time, what I claim as new and desire tosecure by Letters Patent is:

1. A change pitch propeller comprising in combination a blade, a bladeshank that is rotativelymounted in a hub, a couple on the blade shank,an axially expansible two part cam rotatably mounted to po-operate withthe couple 'w'ith one element of' the couple engaging one part of thecam and the other element of the couple engaging 1; other part of saidcam, and means for shifting the cam to change the pitch of the blade. d

. 2. A change pitch propeller comprising in com bination a blade, ablade shank that is rotatively mounted in a hub, a couple on the bladeshank, an axially expansible two part cam rotatably mounted'toco-operate with the couple with one element of the couple engagingone part of the cam 40 and the other element of the couple engaging theother part of said cam, and engine power operated means for shifting thecam to change the pitch of the blade.

33. A change pitch propeller comprisingin com bination ablade, a bladeshank that is rotatively mounted in a hub, a couple on the blade shank,an

' axially expansible two part locking cam rotatably mounted toco-operate with the couple with one element of the couple engaging onepart of the cam and the other elementof the couple engag ing the otherpart of said cam, means for shifting the cam" to change the pitch of theblade and automaticmeans for returning the cam to its flrstposition. i4. In a cam device for changing the pitch of a propeller blade, a couplemade rigid with the blade, a pair of spaced cam engaging elementsthereon, a two part cam member for influencing I the blade, a camslot'in each part engageable with a rigid with the-blade, a, pair of camfingers spaced apart, a two part cam memberfor influencing the blade, acam surface on each part engageable with a cam finger, the two parts ofthe cam member being oppositely axially movable under dyname influencetransmitted from the blade to engage a locking device under positiveload and disengage the said locking device under negative load.

. 6. A changeable pitch propeller comprising in 76.

combination a hub, blade sockets in. the hub,

.blades mounted in the said sockets that are rotatable therein, a camdevice within the hub for selectively rotating the blades, a brakingdevice for displacing the cam in one direction to r0- tate the blades,locking devices operable under dynamic influence received from theblades and spring devicesfor returning the blades to their originalposition upon cessation of dynamic influence.

7. A propeller of prising a propeller hub, blades radial to the hub androtative in sockets formed in the hub, a drive shaft throughthe hub thatis made rigid with the forward end thereof, a two part cam memberloosely mounted on the shaft within the hub, cam engaging devices on theblades that are adapted to change the pitch of' the blades upon relativerotation of the two part cam member, a braking device to retard the cammember with respect to the hub, shaft and blades, devices for lockingthe cam and blades in shifted position under theinfluence-of positiveload that are eifective to unlock the cam under negative load, andreactive means for normally returning the I cam .to its first positionwhen unlocked.

8. In a change pitch propeller having mbvable blades and cam devices fornioving the blades into and out of a plurality of pitch positions, a

brake for moving the'cam, and means for selectively engaging the braketo change the pitch of the blades by retarding the cam to a differentposition with respect to the blades.

9. A two part drum cam for shifting propeller blades that is providedwith centrally disposed intercepting divisional angular surfaces, camsurfaces on both parts of said drum cam, blade shifting devicesengageable with said cam'surfaces, said blade shifting devices beingadapted to move the said drum cam axially to locked position under theinfluence of positive load on the propeller blades.

10. The combination as characterized in claim 9, in which axial relativemovement of the drum cam parts engages relatively fixed locking devicesto retain the said drum cam in adjusted position.

the change-pitch type comsame to revolve.

surfaces on each piece for engaginga couple on a blade and lockingsurfaces incorporated with the cam that are adapted to engageco-operating relatively fixed surfaces by axial movement of the Iretardation.

13. A two pitch propeller comprising a hub, radial bladespivotally'mounted in the hub, a cam member adapted to change the pitchof the blades by relative rotary movement with respect to the hub, meansfor effecting such relative movement and means for reversing saidmovement, the said cam being axially movable to look-- ing engagementwith a relatively fixed part of the hub under dynamic influences fromthe blades when the said blades are under positive load.

14. A two'pitch propeller comprising a hub, radial blades pivotallymounted in the hub,.a two part cam member adapted to change the pitch ofthe blades by relative rotary movement with respect to the hub, meansfor eifecting such rela tive movement and means I for reversing saidmovement, the said cam parts being axially movable to locking engagementwith a relatively fixed part of the hub under dynamic influences fromthe blades when the said blades are under positive load, and axiallyreturnable to unlocked position under the influence of negative load onthe said blades.

15. In a change pitch propeller, a two-part locking cam of the characterdescribed, a gear for moving the cam, a friction wheel for actuating thegear and means for selectively contacting the friction wheel to causerevolution in either direction. I

16. A change pitch propeller defined in part as a hub, blades movablymounted on the hub,

a two-part locking cam within the hub that is operatively connected tothe blades, means integral with the blades for moving the cam to lockedposition under the influence of positive load on the blades, a geardevice for moving said cam to change the blade pitch, a friction wheelfor operating the gear device and means for selectively engaging thefriction wheel to cause the GEORGE McDOUGALL.

